Alice: In the recent years, studies have established that learning and memory abilities as well as mood are influenced by diet. These facts are from a research paper by Muhammad S. A. Zainuddin and Sandrine Thuret.

Nutrition, adult hippocampal neurogenesis and mental health

One of the brain structures associated with learning and memory as well as mood is the hippocampus. Importantly, the hippocampus is one of the two structures in the adult brain where the formation of newborn neurons, or neurogenesis, persists.

Diet quality affects the common mental disorders, depression and anxiety. Diet is also linked with cognitive abilities, especially in the ageing population.

Adult hippocampal neurogenesis (AHN) has been linked directly to cognition and mood; therefore, modulation of AHN by diet could emerge as a possible mechanism by which nutrition impacts on mental health.

Some new neurons die over the next few weeks after they emerged. But some become physiologically mature and functionally integrated in the circuit.

A correlation between the level of hippocampal neurogenesis and the performance in hippocampal-dependent learning tasks is observed between mice with different genetic backgrounds.

Environment is also a major factor.

AHN is reduced by stressful experiences.

AHN is reduced in animal models of depression.

Many treatments for depression have been shown to enhance neurogenesis in laboratory animals. Other environmental interventions conferring antidepressant-like behaviour such as running, exercise and environmental enrichment also increase AHN.

It is apparent that AHN is influenced by neurological diseases or/and that disruption of AHN might contribute to their progression.

Ageing is associated with a decreased AHN, and aged rodents display impaired learning and memory abilities.

Stress is also a major negative modulator of AHN, which can induce depressive behaviour.

Social isolation is a stressful experience in rodents and has been shown to negatively regulate AHN and learning abilities.

Sleep has recently appeared as another important modulator of AHN.

Prolonged restriction or disruption of sleep leads to a major decrease in AHN.

Sleep deprivation (SD) also disturbs memory formation.

! short-term or acute 1-night (12 h) Sleep Deprivation up-regulates AHN by significantly increasing cell proliferation and the total number of surviving cells BUT the negative effect of SD on AHN begins shortly after more than 12 h of SD. In addition, sustained sleep fragmentation has also been found to reduce AHN and caused delayed changes in cognitive function in rats.

Equally, pregnancy and maternal experiences in rodent also have a negative impact on AHN. These are associated with a decline in performance in hippocampus-dependent tasks during pregnancy.

Learning might also induce the activation of newborn neurons and enhance their survival and incorporation into circuits. Indeed, AHN is increased upon learning, but only by learning tasks that depend on the hippocampus

DIET

Nutrition can impact on AHN at four different levels: calorie intake, meal frequency, meal texture and meal content

studies in humans have shown that these same dietary parameters modulate cognitive performance and mood

an interventional trial on memory performance in healthy human elderly subjects has demonstrated the beneficial effects of caloric restriction at 30% for 3 months.

Without modifying significantly calorie intake, extending time between meals increases AHN in mice.

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